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The [[passive-pixel sensor]] (PPS) was the precursor to the active-pixel sensor (APS).<ref name="Fossum2014"/> A PPS consists of passive pixels which are read out without [[amplifier|amplification]], with each pixel consisting of a photodiode and a [[MOSFET]] switch.<ref name="Kozlowski">{{cite journal |last1=Kozlowski |first1=L. J. |last2=Luo |first2=J. |last3=Kleinhans |first3=W. E. |last4=Liu |first4=T. |title=Comparison of passive and active pixel schemes for CMOS visible imagers |journal=Infrared Readout Electronics IV |date=14 September 1998 |volume=3360 |pages=101–110 |doi=10.1117/12.584474 |bibcode=1998SPIE.3360..101K |url=https://www.researchgate.net/publication/268189518 |publisher=International Society for Optics and Photonics|s2cid=123351913 }}</ref> It is a type of [[photodiode array]], with pixels containing a [[p-n junction]], integrated [[capacitor]], and MOSFETs as selection [[transistors]]. A photodiode array was proposed by G. Weckler in 1968.<ref name=fossum93>{{cite journal |last1=Fossum |first1=Eric R. |author1-link=Eric Fossum |title=Active pixel sensors: are CCDs dinosaurs? |journal=SPIE Proceedings Vol. 1900: Charge-Coupled Devices and Solid State Optical Sensors III |volume=1900 |date=12 July 1993 |doi=10.1117/12.148585 |bibcode=1993SPIE.1900....2F |publisher=International Society for Optics and Photonics |pages=2–14 |editor1-last=Blouke |editor1-first=Morley M.|citeseerx=10.1.1.408.6558 |s2cid=10556755 }}</ref> This was the basis for the PPS.<ref name="Fossum2014"/> These early photodiode arrays were complex and impractical, requiring selection transistors to be fabricated within each pixel, along with [[integrated circuit|on-chip]] [[multiplexer]] circuits. The [[noise (electronics)|noise]] of photodiode arrays was also a limitation to performance, as the photodiode readout [[memory bus|bus]] capacitance resulted in increased noise level. [[Correlated double sampling]] (CDS) could also not be used with a photodiode array without external [[computer memory|memory]].<ref name=fossum93/> However, in 1914 Deputy Consul General Carl R. Loop, reported to the state department in a Consular Report on [[Archibald Low|Archibald M. Low's]] Televista system that "It is stated that the selenium in the transmitting screen may be replaced by any [[Diamagnetism|diamagnetic material]]".<ref>Daily Consular Reports No 76–152 Seventeenth Year April, May, June 1914 Page 1731 https://books.google.com/books?id=6VE_AQAAMAAJ</ref>
In June 2022, Samsung Electronics announced that it had created a 200 million pixel image sensor. The 200MP ISOCELL HP3 has 0.56 micrometer pixels with Samsung reporting that previous sensors had
===Charge-coupled device===
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